Feeding ecology and ecological role of rare elasmobranch species in the western Mediterranean Sea

Abstract

The conservation of elasmobranchs depends on accurate biological and ecological data to develop population assessments, ecological risk analyses and ecosystem models. Deficiencies on this information for rare elasmobranch species impair the assessment of their ecological role in marine ecosystem and of management activities necessary to conserve and recover their populations. In this study, we generated new data of the trophic habits of several elasmobranchs poorly studied in the Mediterranean Sea, a highly impacted marine ecosystem. In particular, we combined stable isotope (δ13C and δ15N values) estimates with stomach content analyses to determine the feeding ecology, trophic level and functional role of 11 demersal sharks, 12 skates and 3 electric rays. These species are either cataloged by the IUCN as critically endangered, endangered, vulnerable or near threatened, or are data deficient. Our results revealed differences in the feeding ecology of these species. The rays generally consume small crustaceans, while sharks and electric rays prefer mixed diets composed of cephalopods, crustaceans and fish. Demersal sharks and electric rays showed higher trophic positions than skates. When comparing with other organisms of the ecosystem, results indicated that sharks and electric rays occupy similar positions than other top predators, whereas skates are more similar to medium predators. Based on the δ13C values, a proxy of the habitat used, Somniosus rostratus showed the lowest values indicating that it segregates its foraging area from the rest of studied species